The invention relates to a thermally and mechanically stressed, torsionally rigid connection of two coaxially aligned shafts.
Diverse fields of application are known in which two shafts, which are aligned coaxially with respect to one another, must be connected to one another, and wherein the connecting area is subjected to high temperatures. One such example is a gas turbine in which a first shaft, such as a turbine shaft, is manufactured of ceramic materials, while another shaft which is connected with the first shaft, such as a compressor shaft, is connected to a relatively cooler compressor.
However, applications are also possible in which two ceramic or two metallic shafts must be detachably connected with one another.
Further possible is a case in which a housing division must be avoided. In this case, a one-piece housing may be provided into which two shaft sections are inserted and are connected with one another to form a shaft.
There is therefore needed a connection of this type which can transmit high torque, permit a centering of the two shafts to be connected and, at the same time, may be subjected to high temperatures. In addition, it must be possible to transmit impact forces perpendicularly with respect to the axial direction and to connect shafts with one another which are made of different materials, such as shafts made of different types of ceramics.
The present invention meets these needs by providing a first shaft shoulder formed on an end of one of two coaxially aligned shafts. A second shaft shoulder is formed on an end of the other of the two coaxially aligned shafts with the first and second shaft shoulders being situated opposite one another. First and second elastic intermediate layers are formed on the first and second shaft shoulders, respectively. Two metallic coupling sleeves engage one another, one of the two metallic coupling sleeves being fastened to the one coaxially aligned shaft through the first intermediate layer and the other metallic coupling sleeve being fastened to the other coaxially aligned shaft through the second intermediate layer. A ceramic centering sleeve surrounds the two metallic coupling sleeves and is shrunk onto the two coaxially aligned shafts.
The present invention has the advantages of ensuring an easy centering of the two shafts to be connected even when the temperature is high. At the same time, a torque transmission takes place which is also suitable for impact stresses. An important advantage of the present invention provides for a rotor to be manufactured which comprises two shafts, in which case the two shafts may be connected to form a rotor by means of relatively simple manufacturing measures. As a result, high-cost housing divisions become unnecessary. An arrangement of this type is particularly suitable for turbo-supercharger or gas turbine rotors, where on the one hand a compressor rotor and, on the other hand a turbine rotor must be connected with one another. It is also advantageous that the connection according to the invention can be separated again should one of the two shafts be damaged.
In a preferred embodiment, the two shafts are made of ceramic materials, one shaft being connected with a compressor rotor, and the other shaft being connected with a turbine rotor, or representing the turbine rotor. Alternatively, it is also possible for one shaft to be constructed as an output shaft in order to guide the output from a low-pressure turbine to a power consumption device for example.
As a result of the torque transmission by means of the metallic coupling including two coupling sleeves which engage with one another and which are connected with the shafts by means of an elastic intermediate layer, a certain flexibility is obtained for bridging the expansion differences between the shaft parts and the coupling parts when individual components are acted upon by heat.
The elastic intermediate layer is preferably formed of a metallic fabric which consists of a highly nickel-containing heat-resistant wire cloth. In this case, the wires have a diameter of approximately 0.3 mm. The wires are arranged in a nondirectional manner in a cushion. The layer thickness of the metallic fabric amounts to approximately 3 mm. Inconel x-750, for example, may be used as the material.
The metallic fabric is soldered together with the coupling sleeve and the shaft using a high-temperature solder.
Preferably, the centering sleeve or bush consists of a material which has a lower thermal expansion coefficient than the shaft materials in order to cause a frictional engagement between the two components while the temperature is increased. This further ensures a secure centering of the two shafts. Such a material is preferably also a ceramic material. By means of the frictional engagement, a part of the torque is guided by way of the centering bush, whereby the stressing of the coupling sleeves is reduced. In this case, the thermal expansion coefficient of the centering bush preferably amounts to approximately 0.3 to 0.8 times that of the shafts. Particularly hot-pressed silicon nitride such as HPSN NC 132, is suitable as the material of the centering bush. A slight press fit of approximately 2 to 4 .mu.m is used as the press fit.
Hot-pressed silicon nitride (HPSN), such as CERANOX 206, may be used as the shaft material. A possible alternative is silicon carbide (. . . --SiC) which is less expensive but more sensitive to thermal shock.
However, the invention has broad application to any ceramic or metallic materials forming the shafts, in which case only the elastic intermediate layer must be fixable. The elastic intermediate layers between the shafts, on the one hand, and the coupling sleeves, on the other hand, preferably consist of a metallic fabric or a metallic felt.
Another embodiment according to the present invention provides at least two essentially radial openings in one or in both coupling sleeves so that the axial gap remaining between the two shafts is connected with the exterior space and thus a flow-through of cooling air may be provided. This construction is suitable for reducing the temperature gradients occurring in the shaft.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.